Microscopic Behavior And Properties Of CFRP Interface Under Electrothermal Loading

Carbon fiber reinforced polymers(CFRP)are widely used in civil aircraft structures and are subject to complex environments during service,while low-intensity currents have less concern for CFRP.The research goal of this paper is to obtain the interface temperature of carbon fiber/epoxy composite under weak-current,and obtain the evolution law of the carbon fiber/epoxy interface shear strength and the compression properties after impact(CAI)of the laminate structure under electro-thermal effect.Through analyze the interfacial stress and interfacial physicochemical properties under electro-thermal effect,reveals the evolution mechanism of carbon fiber/epoxy composite performance.The main research contents and results are as follows:The interfacial phase size of carbon fiber/resin composites is very small,the interface temperature under electro-thermal cannot be directly obtained.In this paper,the interface temperature of carbon fiber/resin composite is indirectly obtained by using the temperature-sensitive properties of carbon fiber.When the loading current of monofilament carbon fiber is 0~8mA,the interface temperature varies from 25 to 225°C.The results of monofilament fracture test show that the interfacial shear strength of carbon fiber monofilament/epoxy composite samples increases first and then decreases.The inflection point current intensity is 6mA,the interface temperature reaches 140°C,and the shear strength of the interface increase to 62.39(±1.02)MPa,which is 22.50%higher than the untreated sample.The evolution law of carbon fiber/resin interfacial stress under electro-thermal effect is measured by the change of G’peak of Raman spectroscopy.When the current is 3mA,the interface temperature reaches 65°C,the interfacial compressive stress changes from monotonic increase to monotonic decrease.When the current exceeds 6mA,the interface temperature exceeds 140°C,the G’peak of carbon fiber disappears.In addition,the results of DSC experiments show that the T_g of the carbon fiber/resin interface increases from 80.12°C to 128.54°C at 0~6mA,and T_g begins to decrease when it exceeds 6 mA,and drops to116.78°C at 8mA.The experimental results of IR and XPS reveal the main mechanism of carbon fiber/resin properties,interfacial stress and Tg after electricity.The content of epoxy group and ether bond of carbon fiber/resin changed obviously under loading current.When the current is low,as the current intensity increases,the epoxy group and ether bond content increase,so the stress,T_g and bonding strength of interface are all improved.But when the current intensity reaches 6mA,the interface temperature exceeds 140℃,the fatty ether group in the macromolecular chain of interface component is broken,the crosslinked structure of the polymer is broken down,the G’peak of carbon fiber disappears,so the T_g and bonding strength of interface component both decreased.The carbon fiber/epoxy laminate sample heating-up rapidly under the effect of current,and reach the steady temperature at about 200s.The steady temperature of the sample increases with the increase of current intensity and exceeds 200°C at 35A.The results of impact and CAI experiments show that the impact resistance and the CAI performance of the laminate under electro-thermal reduce slightly and then reduce greatly.The CAI intensity changes from 202.17MPa to 203.96MPa at 0~20A,begins to decrease when the current exceeds 20A,and drops to 146.60MPa at 40A.